[Binding characteristics of RU 486 with glucocorticoid and progestin receptors]

RU 34886 (RU 486) has been proved to fully antagonize the actions of glucocorticoid and progestin at the receptor level. The binding characteristics of RU 486 with the thymic glucocorticoid receptor (GR) and the uterine progestin receptor (PR) were investigated in order to elucidate the mechanism of these antagonistic actions. The ability of RU 486 was studied to promote the "activation" and the "nuclear translocation" of GR and RP. Under heat activation, RU 486 dissociated faster from the activated GR than the non activated, and the binding complex of RU 486 and GR showed lower affinity for DNA-cellulose than the glucocorticoid agonist-GR complex. Nearly undetectable amounts of RU 486 were recovered in the nucleus. Conversely, the RU 486-PR complex showed no difference of dissociation rate between the activated and the non activated condition. Its affinity for DNA-cellulose was the same as that of the activated progestin agonist-PR complex. A large amount of this compound was demonstrated in the nucleus.